1. Field of the Invention
The present invention relates to a method of manufacturing toner particles, toner particles, a two-component developer, a developing device and an image forming apparatus.
2. Description of the Related Art
A toner for visualizing latent images has been used in various image forming processes, and an electrophotographic method may be one of the examples.
In an image forming apparatus of the electrophotographic system, a toner which is electrically charged is fed to an electrostatic latent image formed on the surface of a photoreceptor to develop the electrostatic latent image into a toner image which is, thereafter, fixed on a recording medium to form an image. According to this system, the toner is uniformly attached onto the electrostatic latent image to form an image having a high image density and excellent image quality. From the standpoint of adhering the toner onto the electrostatic latent image, it is important that the toner has even particle sizes, the width of particle size distribution is narrow, and the electrically charging property is uniform. The particle size of the toner affects not only the electrically-charging property but also the reproduction of image of the manuscript maintaining high degree of fineness. The toner having suitably small particle sizes, i.e., particle sizes of about 5 to about 6 μm is effective in obtaining highly finely copied images. Therefore, a study has been conducted extensively to obtain toners having even and small particle sizes. For example, an aggregation method has been known to obtain a toner having even particle sizes. According to the aggregation method, an aggregating agent such as a divalent or trivalent metal salt is added to an aqueous slurry in which fine resin particles, coloring agent particles and releasing agent particles are dispersed so as to aggregate the resin particles, coloring agent particles and releasing agent particles to thereby prepare aggregated particles that serve as a toner. The aggregation method involves problems that must be solved; i.e., excess aggregation takes place forming aggregated particles having too large particle sizes, the aggregation reaction must be conducted for extended periods of time to control the particle size of the aggregated particles, coloring agent particles are unhomogeneously exposed on the surfaces of the aggregated particles causing the electrically charging property of the individual aggregated particles to be dispersed, and releasing agent particles are exposed on the surfaces of the aggregated particles and are melted forming a film that adheres to the surfaces of the photoreceptor becoming a cause of defective image.
In view of the above-mentioned problems, a method of manufacturing a toner has been proposed by aggregating the resin particles and the coloring agent under a heated condition in aqueous medium, for example, in the presence of an aggregating agent, the resin particles being those obtained by polymerizing a polymerizable monomer in the presence of a surfactant having a polymerizable unsaturated group (see, for example, Japanese Unexamined Patent Publication JP-A 2003-345063). According to JP-A 2003-345063, the surfactant having the polymerizable unsaturated group is a non-ionic surfactant having a polymerizable unsaturated group including a vinyl bond. As the aggregating agent, there can be used a divalent metal salt such as alkali metal salt, alkaline earth metal salt, manganese or copper, or a trivalent metal salt such as of iron or aluminum.
There has further been proposed a method of manufacturing capsule particles by a batch system by homogenizing mother particles having a number average particle size of 0.1 to 100 μm and child particles having a number average particle size not larger than one-fifth the number average particle size of the mother particles under an injection pressure of not smaller than 29.4 MPa (300 kgf/cm2) so as to aggregate the child particles on the surfaces of the mother particles (see, for example, Japanese Examined Patent Publication JP-B2 7-75666 (1995)). According to the technology of JP-B2 7-75666, the pressure must be elevated to be not smaller than 54.8 MPa in order to obtain particles having even particle sizes while preventing the occurrence of excess aggregation.
A melt-emulsified aggregation method has been known for manufacturing a fine toner having a small particle size without dispersion in the electrically charging property. According to the melt-emulsified aggregation method, the toner particle size is controlled by passing fine particles through a coiled pipe to impart a centrifugal force thereto in the step of aggregating the fine particles manufactured by a high-pressure homogenizing method.
However, the manufacturing apparatus becomes complex in constitution and requires an increased number of steps driving up the costs of manufacturing.